Section III. [81] Trans. R.S. C. 
A New Method of Determining the Range of Molecular Action and the 
Thickness of Liquid Films. 
By M. M. Garver. 
Presented by JAMES Loupon, LL.D. 
(Read May 16, 1912). 
A reliable method of determining the average distance at which 
molecules act on each other has long been sought. Several methods 
have been employed and have given results that, while not very con- 
sistent among themselves, have yet given values of the same order of 
magnitude. Since the introduction of the electron theory and the view 
of the corpuscular constitution of the atom, the actual dimensions of 
the molecular nucleus as a whole have become a less definite physical 
conception; but the molecule as unit still retains its definiteness of 
character, notwithstanding the changed view as to the constitution of 
the individual atoms which form the molecule. Hence the sphere of 
activity, and the degree of proximity, of molecules in the different phases 
are still regarded as definite physical quantities of a nature to permit 
of numerical estimation in terms of experimentally measured magni- 
tudes. 
In the present paper it is not proposed to review the various at- 
tempts that have been made and the methods that have been used; but 
merely to develop the present theory and illustrate the method of com- 
putation; to give a brief discussion of the new constant in connection 
with the genéral gas equation and make a few general applications of 
the results. In conclusion, a tabulated list of the calculated results 
for a few well-known substances will be appended. 
In 1870 Lord Kelvin ! showed that there is a close dynamical rela- 
tion between the curvature of a liquid surface and the density of the 
saturated vapour in contact with it. I have not seen the original paper, 
hence, must quote at second-hand. Poynting and Thomson? develop 
Kelvin’s conceptions and show how the vapour-pressures of vapours in 
equilibrium with plane and curved liquid surfaces may be expressed 
as a function of the surface-tension of the liquid, the vapour, and liquid, 
densities and pressures. Now all these quantities are definite physical 
constants whose numerical value may be found by more or less accurate 
*Proc. R. 8. E. Feb. 7, 1870. 
*Text-book on Physics. Heat Vol. III p, 317. 

